1. Field of the Invention
The present invention relates to a method for manufacturing a thin film transistor array substrate of a liquid crystal display device, and more particularly, to a method for manufacturing a color filter layer on a thin film transistor array substrate.
2. Description of Related Art
A thin film transistor liquid crystal display (TFT-LCD) mainly comprises a thin film transistor (TFT) array substrate, a color filter substrate and a liquid crystal layer sandwiched therebetween. The TFT array substrate comprises plural pixels in an array, each of which comprises a TFT and a pixel electrode electrically connected to the TFT. Generally, the aperture ratio of a single pixel in the TFT-LCD device directly relates to the quantity of light passing through transparent areas from back light modules. For the TFT-LCD devices having the same power consumption, a higher aperture ratio means a better brightness of TFT-LCD devices.
However, in the process for assembling the TFT array substrate and the color filter substrate, since in practice the black matrix, quite often, cannot align with the color filter accurately, the resulting alignment shift usually causes leakage of light. Hence, in the conventional process for manufacturing a TFT array substrate of an LCD device, the black matrix is designed to be broader than the desired area to be blocked so as to completely inhibit the leakage. However, the aperture ratio of the LCD device is thereby reduced.
In order to obviate the aforementioned problems, a COA (color filter on array) technology has been developed. A COA-TFT substrate of a LCD device is provided to enhance the aperture ratio, and the resolution as well.
FIGS. 1A to 1G are cross-section views of a conventional method for manufacturing a COA-TFT by nine photographic steps. As shown in FIG. 1A, a first metal layer 102 is first formed on a substrate 101 by sputtering, and a gate and other elements of a transistor are defined. Subsequently, as shown in FIG. 1B, SiNx or SiOx as a gate insulating layer 103, a-Si as a semiconductor layer 104, and n+Si as an ohmic contact layer 105 are formed by PECVD, and then a patterned active region is formed by a photographic step. Then, as shown in FIG. 1C, Ti/Al/Ti or Ti/Al as a second metal layer 106 is formed by sputtering, a source and a drain are defined by a photographic step, and the ohmic contact layer 105 is etched to form a through hole by dry etching. As shown in FIG. 1D, SiNx or SiOx as a passivation layer 107 is formed by chemical vapor deposition. Subsequently, a patterned black matrix 108 is formed by coating a photosensitive black resin layer, pre-baking, and then a photographic step.
After the above process, a red filter layer 109 and a contact hole 110 are formed simultaneously by coating a photosensitive red resin layer, pre-baking, and then a photographic step. Subsequently, a green filter layer 111 in the green pixel region, a blue filter layer (not shown) in the blue pixel region, and the contact holes thereof (not shown) are formed by repeating the process for preparing the red pixel region, as the structure in FIG. 1E. Then, an overcoat 112 and a photoresist (not shown) are formed in sequence by coating, and then a contact hole 113 is formed by a photographic process, as the structure shown in FIG. 1F. Finally, as shown in FIG. 1G, a transparent electrode layer 114 is formed by plating, and a patterned pixel region is defined by a photographic step to accomplish the process for preparing a COA-TFT.
As the aforementioned illustration, the conventional process for manufacturing a COA-TFT includes five photographic steps for preparing a TFT array substrate and four photographic steps for preparing a color filter substrate (a total of nine photographic steps). Distinctly, the process for manufacturing a COA-TFT can enhance the aperture ratio, but the complex photographic steps would reduce the yield throughout.
Thereby, in order to reduce the manufacturing cost, and to enhance the yield and the stability of the products, how to simplify the photographic process for preparing a COA-TFT becomes an important issue.